5 research outputs found
Changes of North Atlantic plate motion in early Paleogene driven by Icelandic plume:Insights from kinematic and stratigraphic constraints
No full textMantle convection is a fundamental process that shapes the Earth's surface by providing the driving and resisting forces for horizontal motion of tectonic plates, as well as for inducing non-isostatic vertical motion commonly termed “dynamic topography”. Growing observational constraints of past plate motion and dynamic topography have led to better understanding of the history of surface expression induced by mantle flow. Often these two surface motion signals are studied separately. However, the existence of a thin, mechanically weak asthenosphere allows geodynamicists to link horizontal and vertical motion changes together via mantle flow properties in the context of pressure-driven Poiseuille-type flow. In this paper, we utilize publicly available geologic and geophysical datasets to study early Paleogene plate kinematics and spatiotemporal evolution of dynamic topography in the North Atlantic region. We find that the North America (NAM) and Greenland (GRN) plates experienced a rapid kinematic change around late Paleocene–early Eocene, coinciding with episodes of surface uplift inferred from stage-resolution stratigraphic information around the North Atlantic, Labrador Sea and Baffin Bay. We quantitatively tie these surface motion signals together to underlying asthenospheric flow processes by estimating torque variations on NAM and GRN. These are parameterized in terms of reconstructed kinematic changes as well as predicted Poiseuille-type flow induced by increasing Icelandic plume flux and speedup of Farallon slab. Our analysis indicates (1) that the torque-change associated with the Icelandic plume flux closely resembles the ones inferred from kinematic reconstructions, and (2) that the inclusion of slab effects does not modify significantly such a scenario. Our findings shed light on the role of asthenospheric channelized flow generated by the Icelandic plume in influencing the early Paleogene North Atlantic surface dynamics
Depth-dependent azimuthal seismic anisotropy governed by Couette/Poiseuille flow partitioning in the asthenosphere
No full textAzimuthal seismic anisotropy provides crucial knowledge on spatial patterns of past and present upper mantle deformation. Origins of this deformation were traditionally tied to relative shear between surface plates and mantle, and in turn a constant orientation of anisotropy azimuths with depth. However, observations of azimuthal seismic anisotropy based on surface-wave tomography often feature depth-dependent azimuths in the upper mantle. This is consistent with the existence of low-viscosity, thin asthenosphere that facilitates the channelization of both plate-driven Couette flow and pressure-driven Poiseuille flow. If the two flows are not aligned, their combination yields depth rotations of asthenospheric shear, giving rise to depth dependence of azimuthal seismic anisotropy. In this study, we utilize publicly available azimuthal seismic anisotropy together with predictions from a global mantle flow model that incorporates Couette/Poiseuille flow. We find that Poiseuille flow has significant influence on depth rotations of seismically inferred azimuthal anisotropy. Depth rotations are prominent under the Atlantic basin and the Nazca plate, where modeled asthenospheric flow regimes are dominated by Poiseuille flow. Significant Poiseuille flow may exist beneath the Indian basin, but its depth rotations are small, probably because subduction zones to the north align Couette and Poiseuille flows into the same direction. Our results indicate that interpretation of azimuthal seismic anisotropy cannot be simply associated with relative shearing between plates and mantle. Instead, the relative importance of Couette and Poiseuille flows must be considered to account its depth dependence.</p
Oligocene North American kinematic change driven by Canary plume activity
No full textProgressively denser mapping of ocean-floor magnetization has led to detailed reconstructions of past plate motions in the Cenozoic. These reconstructions often reveal rapid kinematic changes that provide crucial information for identifying geodynamic mechanisms that may have caused them, and for quantifying force budgets upon plates. In parallel to these advances, the notion of thin, low-viscosity asthenosphere beneath tectonic plates that facilitates their motions has emerged and consolidated. This weak, mobile layer promotes the formation of the pressure-driven Poiseuille flow that, in turn, generates basal shearing upon plates. In addition, it can be linked to dynamic topography variations due to pulsing plume activity. In this study, we use publicly available finite-rotation compilations of the North American plate (NA) to investigate its kinematic history since Oligocene time. After removing data that are possibly impacted by significant noise, we find that NA experienced a westward speedup near 27 Ma. Next, we explore the role that asthenospheric Poiseuille-type flow caused by increased Canary plume activity may have had in generating this kinematic change. Such plume activity is inferred from the combination of anomalously shallow residual bathymetry and records of past ocean-floor magmatism offshore northwestern Africa. We compare estimates of torque variation upon NA that are (i) required to explain the reconstructed kinematic change, and (ii) predicted by the Poiseuille-type flow associated with the Canary plume activity. Our results indicate that these two torque-variations estimates are in agreement with each other, both in terms of direction and magnitude. This inference suggests that the increased Canary plume activity is a geodynamically-plausible process to explain the Oligocene plate-motion change of NA.</p
Cenozoic upper mantle flow history of the Atlantic realm based on Couette/Poiseuille models: Towards paleo-mantle-flowgraphy
No full textMantle convection is a fundamental process in the Earth's system, yet its history remains poorly known. Sophisticated inverse geodynamic Earth models are available to retrodict past mantle states, but their high computational cost and complex parameterizations limit their ability to isolate key effects and interpret simulated paleo-mantle-flow patterns. This calls for an approach to conceptualize paleo-mantle-flow at a simple analytical level. The existence of weak asthenosphere allows one to formulate a Couette/Poiseuille model of upper mantle flow, where flow is linked to movements of overlying tectonic plates, and to lateral pressure gradients induced by rising plumes and sinking slabs. Here we present results from such models for the Atlantic realm in the Cenozoic, and link them to seismically inferred anisotropy along with mantle flow retrodictions from inverse geodynamic modeling. Our analytical paleo-mantle-flow indicates that (1) material sourced by plumes is carried towards slab locations, as expected, (2) it is broadly consistent with the orientation of seismic azimuthal anisotropy, and (3) it agrees with the large-scale flow patterns and amplitudes from mantle flow retrodictions. Our results suggest using a hierarchy of models together with growing geological constraints on past plate motions and dynamic topography to gain a better understanding of paleo-mantle-flow.</p
Alkali metal storage mechanism in organic semiconductor of perylene-3,4,9,10-tetracarboxylicdianhydride
No full textOrganic semiconductor-based electrode materials are promising candidates for energy storage devices due to their high capacity, excellent flexibility, low cost and resource sustainability. The alkali metal storage mechanisms on various active functional groups of the organic materials, however, are still not clear at the molecular scale. It is essential to conduct systematic mechanism studies for the alkali storage behaviors in organic electrode materials. Here, the chemical and electronic structure evolutions upon the deposition of lithium (Li) and sodium (Na) on a model organic semiconductor electrode material of perylene-3,4,9,10-tetracarboxylicdianhydride (PTCDA), have been investigated by in-situ x-ray photoemission spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), near edge x-ray absorption fine structure (NEXAFS) spectroscopy and density functional theory (DFT) calculations. It reveals that Li/Na can react with the carbonyl oxygen and increase the electron density within the PTCDA perylene. Moreover, the band-bending like features are observed on PTCDA film upon Li/Na interaction. Our experimental results and theoretical calculations indicate that reactions on carbonyl groups and charge redistribution are crucial for the Li/Na storage process, which shed light on comprehensive insights for the Li/Na storage behaviors on organic semiconductor-based electrode materials.Ministry of Education (MOE)Authors acknowledge the financial support from Singapore MOE grant R143-000-A29-112 and Academic Research Fund Tier 1 (RG104/ 18), as well as the computing resources from National Supercomputing Centre Singapore
